Recently, a device in which an LED element is used as a light source is in practical use with improvement of optical performance of a Light Emitting Diode (LED) element. For example, a DC LED lighting device in which a switching means is utilized is widely used as an LED lighting device that lights the LED element.
Conventionally, for example, a transistor made of an Si (silicon) semiconductor is used as the switching means (switching element) of the LED lighting device. A transistor in which a wide-bandgap semiconductor such as SiC (silicon carbide), GaN (gallium nitride) and diamond is used receives attention.
Generally a wide-gap semiconductor has a normally-on characteristic in which a current is passed when a gate voltage is zero. Examples of the semiconductor element in which the wide-gap semiconductor is used include a JFET (Junction type FET), an SIT (Static Induction Transistor), an MESFET (Metal-Semiconductor FET: Metal-Semiconductor-Field-Effect-Transistor), an HFET (Hetero junction Field Effect Transistor), an HEMT (High Electron Mobility Transistor), and a storage type FET.
In order to securely turn off the semiconductor element (hereinafter referred to as normally-on switch) having the normally-on characteristic, it is necessary for the LED lighting device to comprise a control circuit for negative gate voltage.
There is well known the fact that the LED lighting device having high circuit efficiency is obtained by lighting the LED element with a DC-DC converter. In the DC-DC converter, a switch element is driven using an induced electromotive force, which allows constant current control to be performed.